Refrigerated display cabinet and method of operation



S` BECKWITH March 3, 19264 REFRIGERATED DISPLAY CABINET AND METHOD OF OPERATION Filed` April 9, 1962 2 Sheets-Sheet l N www Xml Ilww

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REFRIGERATED DISPLAY CABINET AND METHOD oF OPERATION Filed April 9, 1962 2 Sheets-Sheet 2 l l l l 1 SJODRM l 4 5 l 12 '1r I 1 l I l l l t l (I l2 i i 12:00am e l `l l I l I l I l l l I 9:00AM I l 1 L A' i l l 6:00AM l n' |000 :I5-n [00 INVENTOR.

United States Patent O 3,122,892 REFRIGERATED DISPLAY CABENET AND METHOD OF OPERATION Sterling Beckwith, Libertyville Township, Ill., assigner,

by mesne assignments, to Dual 5 et Refrigeration Company, a corporation of illinois Filed Apr. 9, 1962, Ser. No. 186,019 1G Claims. (Cl. 62-81) This invention relates to a refrigerated open display cabinet and more particularly to an upright cabinet having an open front wall of an otherwise enclosed refrigerated storage space for visual and for actual access to the space for observation of the contents thereof and for the displacement of content material into and out of the refrigerated storage space.

This invention is addressed to a refrigerated display cabinet and the operation thereof wherein the cabinet is formed with a refrigerated space having a front, vertically disposed wall which remains continuously open to the atmosphere to enable displacement of products into and out of the refrigerated space. The space is maintained in a desired refrigerated state by the use of an air curtain formed of an inner panel of cold refrigerated air and one or more outer guard panels of air of increasing temperature with the air curtain traveling across the open space from one edge to the opposite edge completely to separate the refrigerated space from the atmosphere.

F or more eiicient operation, it has been found desirable to recirculate at least the cold air making up the cold air panel of the air curtain and preferably the air in the cold air panel and the air in one or more of the adjacent guard panels whereby the horsepower of refrigeration required to maintain the desired temperature level within the refrigerated space is greatly reduced and whereby refrigeration means can be incorporated in the passages through which the air streams are recirculated for purposes of removing heat from the air stream or streams passing therethrough to reduce the temperature of air forming the described panels. Such means for the removal of heat from the air stream or streams making up the inner cold air panel and adjacent guard air panels usually comprises evaporator plates mounted Within the passages through which the respective air streams are circulated with the evaporator forming a part of a refrigeration system through which a liquid refrigerant is circulated.

While it would be ideal to maintain complete separation of the air panels making up the air curtains, the necessa f larninar flow characteristics between adjacent panels is diiiicult to achieve. It is estimated that as much as -20 percent intermixing of air can take place between adjacent panels under normal operating conditions, depending somewhat upon the nozzle construction, air velocities, distance across the open space and cabinet construction. Such intermixing results in some of the air from the ambient atmosphere progressively migrating from the outermost panel through intermediate air panels to the cold air panel whereby the temperature is gradually reduced to the point where the amount of moisture in the air making up the colder air panels is in excess of that capable of being retained in the air stream so that some moisture deposits as frost upon cold surfaces, such as the evaporator plates or other surfaces impacted by the air stream, such as the air nozzles from which the air panels are projected across the open space.

Such accumulation of frost on surfaces within the air passage will be found to interfere with the laminar ow characteristics of the air stream or streams across the open space and with the refrigeration of the air traveling through the air passages. It is desirable to eifect frost removal to avoid such interference but it is desirable t0 effect frost removal in a manner to have minimum effect ice upon the maintenance of the refrigerated state within the refrigerated space.

Thus it is an object of this invention to produce a refrigerated display cabinet of the type described and a new and improved method for the operation of same and it is a related object to provide a new and improved cycle of operation for use in a refrigerated display cabinet of the type described.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of this invention is shown in the accompanying drawings, in which,

FIG. l is a schematic sectional elevational View of a refrigerated display cabinet embodying the features of this invention;

FIG. 2 is a sectional elevational view of a modification of the refrigerated display cabinet shown in FIG. l;

FIG. 3 is a schematic flow diagram of a refrigeration and defrost system employed in the practice of this invention; and

FG. 4 is a reproduction of a recording chart showing the temperature conditions existing in various parts of the refrigerated display cabinet during a cycle of operation.

Before entering into a detailed description of the operation of the refrigerated display cabinet and its refrigeration system, reference will be made briefly to the construction of the cabinet and some of its various modifications.

The cabinet is in the form of a housing having a top wall l2, a back wall 14, a bottom wall 16, side walls (not shown) and a front wall 1S. The front wall is provided with an access opening 20 of substantial dimension for communication of the enclosed space 22 within the interior of the housing with the outside atmosphere. The cabinet may rest upon a suitable base 24.

Spaced inwardly from the outer walls of the housing and arranged in substantially parallel relationship therewith are inner walls including a top wall 26, back wall 28, bottom wall 3?, front wall 32 and side walls 34, all of which define a storage space 22 therebetween.

The space between the inner walls and outer walls of the cabinet are subdivided by spaced partitioning walls 36 and 37 to dene three separated passages 38, 4l) and 41 which extend continuously about the storage space 22 from inlet openings 42, i4 and 45, extending continuously across the bottom edge of the access opening 20, to outlet openings 46, 48 and 49, extending continuously across the opposite or top edge of the access opening.

The passage 38 is provided with evaporator coils 5i) through which a `suitable refrigerant is circulated for passage in indirect heat exchange relationship with the air traveling through the passage 3S for the refrigeration thereof. Nhile the evaporator coils or plates 59 are illustrated las being located in the bottom run of the passage 3S, adjacent the inlet 42, it will be understood that the refrigeration means can be disposed in other parts of the passage. located in advance of the evaporator coils 59 land preferably between the evaporator ycoils and the inlet 42, is `an air circulating means, such as a fan or blower 52, which operates to induce the flow of a stream of air through the passage 38 from the inlet 42 to the outlet do and, in accordance with the concepts of this refrigerated display cabinet, from the outlet d6 across the access opening 2d to the inlet 42 for recirculation of the inner cold air stream.

Similarly located within the passage 40 is an auxiliary refrigeration system including evaporator coils 53 through which refrigerant is adapted to be recircuiated and the passage 40 is also provided with `an air circulating means 54, such as a fan or blower, for inducing the flow of air through the passage dit from the inlet 44 to the outlet 48 and then from the outlet 48 across the access opening 20 3 .to the inlet 44 for recirculation of what will hereinafter be referred to as the guard jet.

lrPhe passage 41 is merely provided with a `fan or blower 55 for inducing the flow of air from the inlet 45 through the passage 41 to the outlet 49 and then from the outlet 49 across the access opening 2i) to the inlet 45 for recirculation as a second guard jet. llt will be understood that the refrigerated display cabinet can be eectively operated Ywithout .the evaporator coils 53 in the passage 49 for refrigeration of the guard stream of air making up the guard jet and .that the cabinet may also be effectively operated without the passage 41 and its corresponding inlet 45 and outlet 49 and that, by way of still further -modilicatiom the refrigerated display cabinet may be constructed with still further passages and associated inlets and outlets to increase the number of guard iets, `where practical, with the corresponding improvement in laminar ow characteristics between the air panels mal;- ing up the air curtain traveling from the outlets to the inlets across the access opening and with corresponding improvements .also being experienced in the reduction of heat loss from the interior .of the cabinet to the ambient atmosphere.

Outlets `4-5, 4S and 4? are provided with nozzle members 56, 58 and 59 constructed directionally to channel the air streams issuing therefrom for substantially laminar flow .across the access opening from the outlets to the inlets, as previously described. lFor this pur-pose, the nozzles may be constructed of vaned members, such as a honeycomb section, preferably having an effective length greater than about l inch and up to about 5 or 6 inches. The streams of air issuing from the outlets 46, 48 and 49 form vcontinuous inner and outer air panels 60, V62 land 63 which extend across the access opening 2@ from the outlets to the inlets with the inner panel 60 representing the refrigerated or cold air panel adapted to maintain the storage space in the desired refrigerated state. The inlets can be provided with screening members 64 to protect the passages against the .entrance of insects, foreign material and the like.

From the `foregoing brief description of the basic construction of the refrigerated display cabinet, it will be apparent that there is provided an inner cold `air panel 6% and outer guard panels 62 and 63. The guard panel 62 will acquire a temperature Iintermediate the temperature of the cold air panel 60 and the temperature of the guard panel 63 lwhile the guard panel 63 will acquire a temperature .intermediate the guard panel 62 yand the ambient atmosphere by reason of the small amount of intermixing that normally occurs between the panels flowing next to each other in a combined curtain. The refrigeration of the space 22 is also achieved in part by the flow of the cold air stream through the passage 38 in substantially heat exchange relationship with the storage space. Further to minimize heat loss, the partitioning walls 36 and 37 can Xbe provided with suitable insulation, as indicated by the numeral 66.

Because of the marked reduction that takes place in the temperature of the air as it is displaced gradually from the ambient Iatmosphere kthrough the outer guard panels to the cold air panel, it will be apparent that the relative humidtiy of the air will 4be increased to the eX- tent that the air making up the cold air panel will reach a state whereby moisture will be deposited in the form of frost onto cold surfaces engaged by the air stream.

Referring now to FIG. 3 of the drawings, the evaporator plate Si) in the cold air passage 38 and the evaporator plate 53, when employed in the guard air passage, are provided with drain pans 91 and 93 respectively and with drain pipes 9d and 92 respectively. The other elements conventionally employed in a refrigeration system include a compressor 104, a condenser 1%, and a receiver v1li-8 whereby, during the refrigeration cycle, liquid refrigerant 110 is advanced from the receiver through line 112 to a. drier 114 and from the drier through line 116 to a heat exchanger '118 and then through line 12@ to a solenoid valve 122 which controls `the passage of refrigerant liquid to the evaporator coils 5) and/or 5t) and 53. The refrigerant vapors from the evaporator coils pass through line 124 through the heat exchanger 118 to the compressor 194 where the vapors are recompressed and advanced through line 12S to the condenser 106 wherein the compressed refrigerant vapors are condensed to the liquefied state for return through line to the receiver 1%.

vVarious techniques have been employed for defrosting the evaporator coils in a refrigeration system. One such technique, employed in the practice of this invention, is 'often referred to as hot gas defrost wherein the refrigerant vapors issued from the .compressor and heated -up by the *work formed in compression are recirculated through the evaporator .coils yfor rapid Vheat transfer to melt .the frost collected on the surfaces thereof. .Sometimes the heat introduced into the .exhaust gases by the compressor is suplemented by external heat supplied in heat exchangeV relationship with the hot gases advanced through the line 132 to the evaporator coils.

Tlhe defrost cycle, using the conventional Vhot gas defrost, may require a length of .time which permits changes to take place in the temperature conditions existing Within the refrigerated space. It has been found that the defrost cycle can bel markedly improved by modification of the hot gas defrost system greatly to increase the volume of hot gases which are circulated through the evaporator coils. While the concepts of this .invention include the concepts of the conventional hot gas defrost within its new and novel cycle of operation, it will be understood that the improved rapid defrost hereafter to be described is preferably employed in the cycle of operation-s of the refrigerated display cabinet.

For more rapid hot gas defrost, there is provided an auxiliary supply of refrigerant liquid in communication with the discharge line 130 or 132 whereby the pressure conditions existing when the hot gases from the compressor are recirculated to the Vrefrigeration coils during the hot gas defrost cycle, draw the refrigerant liquid from the .auxiliary supply into the lead line 132. Auxiliary heaters 134 are provided in heat exchange relationship with Vline 132 to reduce the refrigerant liquid to the gaseous state thereby materially to increase the volumetric heat llow of gases to t'he evaporator coils. The quantity increase of heat Vflow of hot gases to the evaporator oper- .ates materilly to reduce the defrost cycle to a matter of but .a few minutes compared to more than three or four `times yas long in conventional hot gas defrost systems.

ln the Villustrated modification, the auxiliary refrigerant liquid is collected in a pan 135 mounted within the receiver 108 and in communication with the outlet of the line 136 so that the condensed refrigerant liquid is rst deposited into the pan yto fill vthe pan before the Voverflow passes into the receiver. Thus the pan is immediately relled with refrigerant liquid during the normal refrigeration cycle and it can be dimensioned to hold an amount of refrigerant liquid capable of supplying the additional volume of gases for defrost. Usually, an auxiliary supply of from l() to l2 pounds will be suiicient. Instead of collecting the refrigerant liquid in a pan disposed within the receiver, the auxiliary liquid can be supplied in a container separate and apart from the receiver but which communicates with the line 132 through which the hot exhaust gases are advanced to the refrigeration coils for defrost.

In operation, the defrost cycle is initiated by an electrical signal which may be'responsive to the frost build-up on the evaporator coils or to a temperature differential control or to a timer or other conventional means for signaling the termination 'of a refrigeration cycle and the initiation of the defrost cycle. In sequence with the signal, the liquid solenoid valve 122 is closed to shut off flow of refrigerant liquid in the evaporator coils. After a short period for vaporization of the refrigerant liquid remaining in the coils, the suction solenoid valve 136 is closed and simultaneously the hot gas solenoid valve 138 is opened whereby the hot gases exhausted from the compressor are recirculated through line 132 to the inlet side of the evaporator Sil.

In conjunction with the opening of the hot gas solenoid 138, a pressure drop occurs which draws or otherwise forces a small quantity of auxiliary refrigerant liquid from the auxiliary supply 13S into the discharge line 130 and hot gas line 132. As the auxiliary liquid is advanced through the air cooled condenser 106 and the hot gas line 132, the heating means 134 operates to vaporize the liquid and to heat the vapors whereby the auxiliary refrigerant liquid is converted into a large volume of hot gases. The total heat of the hot gases exhausted from the compressor and the hot gases of the converted refrigerant liquid is advanced through the line 132 to the evaporator. The heat from the total volume of hot gases is absorbed by the evaporator coils to cause rapid melting of the frost collected on the surfaces thereof. The liquid is drained from the surfaces of the evaporator coils into the pans 91 or 93 and removed from the refrigerated cabinet through the drain pipes 90 or 92.

The hot gases are condensed for reconversion into the liquid form which accumulates in the suction line side of the evaporator. A capillary tube 140, which bypasses the suction solenoid valve 136, operates to discharge the accumulated liquid into the suction line 124 for return to the compressor.

Having brieiiy described the construction of the refrigerated cabinet and the concepts of its operation and having briefly described the refrigeration and defrost system, description will now be made of the operation or" the cabinet and its refrigeration system in a complete cycle of operation whereby minimum effect upon the maintenance of a desired refrigerated state within the refrigerated space can be achieved. For this purpose, the refrigeration cycle is interrupted at relatively frequent intervals for only a short period of time for defrosting the evaporator coils and at relatively remote intervals for a longer defrost period substantially completely to defrost additional areas which are subject to frost formation and er'tect upon the ow of ah forming the cold air panel. ln this way, frost is prevented from accumulating to the extent of interfering with the low characteristics of the cold air stream and such protection is achieved while still maintaining almost continuous ow of the cold air stream more than for only very short periods of time thereby making it necessary for a complete defrost cycle to be so spaced that the latter can be carried out less frequently and at periods of time when the cabinet is not in use for the dispensing of pro-ducts. As a result, it becomes possible to effect the complete defrost in the evening or early morning every 24, 48, 72, etc. hours, as a particular situation may dictate, and when it becomes possible to enclose the refrigerated space for maintenance of the refrigerated state therein.

For purposes of illustrating the temperature conditions existing during a complete cycle of operation of the refrigerated display cabinet, thermocouples have been located in various parts of the cabinet and the refrigeration system and the temperature changes taking place in response to the changes in conditions during the cycle of operation have been recorded on the chart illustrated in the drawings by FIG. 4.

Thermocouple 1 has been located within the refrigerated space to measure the temperature therein. Thermocouple 3 has been located as close as possible to the inner side of the air curtain to measure the temperature of the cold air panel. Thermocouple 4 has been located at the ingoing side of the evaporator coil to measure the temperature of the'refrigerant liquid entering the coil. Thermocouple 5 has been located at the outgoing side of the evaporator coil to measure the temperature of the refrigerant vapors leaving the coil. Thermocouple 6 has been located at the outlet of the outer guard air panel 63. Thermocouple 7 has been located at the outlet for the cold air panel for measuring the temperature of the air forming the cold air panel. Thermocouple 10 has been located in the cold air passage between the inlet and the evaporator coil to measure the temperature of the air beforeV passage in heat exchange relationship with the evaporator coil. Thermocouple 11 has been located at the outlet for the guard air panel 62 to measure the temperature of the air making up the guard ah panel. Thermocouple 12 has been located between the inlet to the guard air passage and the evaporator coil to measure the temperature of air before passage in heat exchange relationship with the evaporator coil. Thermocouple 13 has been located in the passage 41 for the outer guard air panel. Thermocouple 15 has been located outside of the cabinet to measure the wet bulb temperature, and thermocouple 16 has been located outside the cabinet to measure the dry bulb temperature.

Before the intermediate defrost, the cabinet will have reached a relatively constant refrigerated state wherein, as shown `along the line AA of the chart of FIG. 4, the temperature of the refrigerant entering the evaporator `(therrnocouple No. 4) is about h 35 F. while the exit temperature of the refrigerant vapors is at about -25 F. (thermocouple No. 5). The temperature of the outer guard jet (thermocouple No. 6) is about 50 F., the temperature of the guard jet is about 35 F. (thermocouple No. 11), and the temperature of the cold air jet at the outlet nozzle l(thermocouple No. 7) is about -20 F. The temperature of the guard air, after crossing the open space, is about F. (thermocouple No. 12) or slightly lower than the air issuing from the nozzles 48 because of the cold air admixed from the cold air stream. The temperature of the air entering the passage 38 is about -10 F. (thermocouple No. 10) because of the warmer air admixed from the guard jeft. The temperature within the chamber is about 5 F. to -l0 F. (thermocouples Nos. 1, 3 and 14). Thus a temperature below freezing is maintained within the refrigerated Space.

The following is the sequence of steps as related to time as they `occur in the operation of the refrigerated cabinet for effecting an intermediate defrost every three hours:

Time cycle Operation: (in minutes) (l) Top coil solenoid 122 is closed 0:0

y(2) Heater 134 in advance of the vaned outlet 56 is turned on 0:50 (3) Front and back dampeners 201, 262, 263

and i204 are closed to stop the flow of air through passages 38 and 40 1:10 (4) Suction solenoid 136 is closed to block flow of refrigerant vapors ,1: (5) Hot gas solenoid '13S is opened to recycle hot gas exhaust from the compressor to the evaporator 1:50 minutes 31/2 (6) Hot gas 4solenoid y13S is closed to terminate hot gas defrost 5 :20 (7) Front and back dampeners 201, 202,

203 and 204 are opened to resume air flow 5 :30 A(8) Suction solenoid 136 is re-opened 5:50 (9) Top coil Sil liquid solenoid 122 is opened to resume circulation of liquid refrigerant to the top evaporator coil 50 6:20 (l0) Heater 134 is turned oli 6:40 (ll) Bottom coil 513 solenoid 12.2a is opened to circulate liquid refrigerant to bottom refrigerator coils 53 in passage 40 to cool the guard jet :0 (l2) Bottom coil liquid solenoid 12.2a is closed to shut off refrigerant to the bottom coil 53 180:0

Y (13) Cycle repeats itself after the 180 minutes until lthe major defrost cycle which is adapted to take place every 24 hours as follows:

(l) Top coil solenoid 122 vis closed 0:0 (2) Heater 134 in advance of nozzle 56 is turned on to remove frost from the nozzles 0:50 V( 3) lFront and back dampeners 2M, 262,

203 and 204 are closed to stop air circulation through passages 38` and et?" 1:10 (4) Suction solenoid 136 is closed 1:35 (5) Hot gas solenoid I21.38 is opened )1:50

(s) Hot gas solenoid is is mmutes" 17 closed 18:50y (7) Front Vand back dampeners 2011, 2%2,

293 and 284 are opened 21:20 (8) Suction solenoid 135 is opened 21:20 (9).Top coil liquid solenoid 122 is opened 23:50 Heater i3d is shut off 25130 V(ll) Bottom coil liquid solenoid T2211 is opened 512.0:0 (l2) Bottom coil solenoid 122 is closed 180:0

It will be apparent from the foregoing that when the refrigerant is circulated through the coil 53 in the guard passage 40 about one hour before either the long or short defrost cycle, the temperature of the cold air stream shifts slightly upwardly from about 25 F. to about 20 F. while the temperature in the guard stream shifts downwardly from about 35 F. to about 201 F. at the outlet and about 23 F. at the inlet. The latter is below freezing temperature -with the result that some moisture is taken out of the guard air stream by condensation on the coils S3 thereby to minimize the amount of frost build up on the surfaces of the coils 5@ in the cold air passage. This is achieved without sacrifice of temperature in the cold air stream which, as previously pointed out, rises from about 25 F. to about 20 F. which is still far below freezing. -It enhances the rate of defrosting by materially reducing the amount of frost formation on the coils 50. The temperature of the cold air stream entering the passage 3S is affected but slightly, being raised Vfrom about 8 F. to about 6 F.

During the extended defrost cycle, carried out every 24 hours in the foregoing illustration, temperature changes of greater magnitude take place. The temperature of the `outer guard jet rises to a maximum of about 60 F. and then rapidly returns to the normal of about l5-50 F. when the refrigerant is again circulated through the coils and the dampeners opened.' The guard jet also rises in temperature Vfrom F. before the defrost cycle to a maximum of about 45 F. during the latter stages of the defrost 'cycle and then returns to a temperature of about 35 F. during the initial stages of the refrigeration cycle until refrigeration of the guard jet about one hour before either the intermediate or major defrost, as previously pointed out.

The cold air stream is completely shut off during the defrost cycle and when the cycle is resumed, the cold air temperature starts out at about 5 F. and is reduced rapidly to the normal of about F. over the next two hours.

During the short intermediate defrost cycle, which in the illustrated modification is effected every three hours for rapid defrost of the coils of the evaporator in the cold air stream, the temperatures are affected still less. The outer guard stream rises but a few degrees from 45 F. to about 48 F. The guard jet rises from about 20 F. to about F. until the guard stream is refrigerated, and the cold air stream drops from about 20 F. to about 25 F. because of the shutoff of refrigerant to the guard jet and the continued cooling of the cold air stream. The foregoing cycles are given by way of illustration of the preferred sequence of steps in the operation of the refrigerated cabinet. The description is Vnot to be considered as a limitation `as t-o the times since the sequence of steps can be spaced over a shorter or greater distance, depending upon the atmosphere conditions existing in the particular locality. Where the outside temperature is cold or where the humidity is low, the time cycle can be extended. Where the humidity is high, then the defrost cycles can he brought closer together.

The description makes reference to a construction of cabinet illustrated in FIG. 2. wherein the dampers 201, 292, 263 and 264 block the passages on opposite sides of the evaporator coils. It is sometimes preferred t0 make use of the construction shown in FIG. 1 wherein the dampers function as cross-over dampers whereby ywhen the damper 76 lis opened, it operates to deect the cold air stream from the passage 38 through the connecting passage 77 into the kguard air passage 4i) While, at the same time, the damper 7S deflects the guard stream from the passage 40 through the cross-over passage 79 to the cold air passage 33. At the same time, the dampers $6 and -88 on the other side of the evaporator-s 50 and 53 operate to return the cold air stream from the passage e@ to the passage 38 and return the guard air from the passage 3S to the passage 40. Thus the cold air stream and the guard air stream can be maintained in constant circulation while the guard air stream, at above freezing temperature, assists the hot gases in 4defrost of thercoils 59. Such frost as is formed on the evaporator coils 53 in the interim is removed when the streams yare returned to their normal passages after the defrost cycle.

It will be apparent from the foregoing that I have provided a new and novel cycle of operation for an opensided refrigerated display cabinet and method for the operation of same.

It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as dened in the following claims.

I claim:

1. In the method of refrigeration of a space which is enclosed except for a side having an access opening directly communicating 4the interior of the space with the ambient atmosphere, the steps of circulating inner and outer air panels in side-by-side, substantially parallel relationship across the open space from one edge of the open space to the opposite edge substantially completely l to span the open space with the formed air curtain, separating the air panels upon reaching the opposite edge, recirculating the separated air panels from the opposite edge back to the one edge, passing the recirculatingV inner panel of air in heat exchange relationship with refrigeration coils through Iwhich a refrigerant is circulated to reduce the temperature of the air making up the inner panel to a cold air stream, periodically between relatively short intervals of time stopping the circulation of the air panels and for a short period of time While the circulation of the air panels is stopped, defrosting the `refrigeration coils, and periodically between relatively long intervals of time stopping the circulation of the air panels and for a relatively long period of time defrosting the .refrigeration coils.

2. The method as claimed in claim 1 which includes the step of, for a period of time, prior to the stoppage of the circulation of the yajr panels `andthe defro-sing of the refrigeration coils in heat exchange relationship with the recirculating cold air stream, passing the outer panel in heat exchange relationship with refriger'ating coils through which a refrigerant is circulated temporarily further to reduce the temperature of the air stream making up the outer panel of air.

3. The method as claimed in lclaim 1 which includes the step of, during the time that the recirculation of the cold rair stream is stopped for defrosting, introducing t heat to the outlet through which the cold air stream issues from the one edge across the open space to remove frost from the area from which the cold air stream issues from the one edge across the open space.

4. The method as claimed in claim 1 in which in the refrigeration cycle a liquid refrigerant is circulated from a source of supply to the refrigeration coils wherein the refrigerant liquid is converted to a Vapor state upon the absorption of heat, said vapors being recirculated from the refrigeration coils to a compressor where the vapors are compressed and then passed in heat exchange relationship with a coolant wherein the compressed vapors are reduced to a liquefied state for return to the supply source, the step of circulating the hot exhaust vapors from the compressor to the refrigerating coils during the defrosting step for more rapid defrost or the coils.

5. The method as claimed in ciaim 1 in which additional outer air panels are circulated in side-oy side, substantially parallel relationship with the inner and outer panels of air to malte up the air curtain projected across the open space and in which the additional air panels assume temperatures intermediate the outer air panel and the ambient atmosphere.

6. The method as claimed in claim 5 in which one or more ofthe additional air panels are separated and recirculated from the opposite edge to the one edge across the open space.

7. ln the method of refrigeration of a space which is enclosed except for a vertical side having an access opening of substantial dimension directly communicating the interior of the space with lthe arnoient atmosphere, the steps of projecting an inner cold air panel and an outer guard air panel in side-by-side, substantially parallel relationship yfrom one edge of the open space to the opposite edge of the open space substantially completely to span the open space with the formed air curtain, separating the cold air panel from the guard air panel at the opposite edge of the open space, recirculating the separated cold air panel through a passage communicating the opposite edge ywith the one edge of the open space and recirculating the guard air stream through a separate passage communicating the opposite edge with the one edge across the open space, projecting evaporator plates within each of said passages whereby the recirculating air streams pass in heat exchange relationship with said evaporator plates, circulating a refrigerant through the evaporator plate in the cold air passage to reduce the temperature of the cold air recirculated therethrough, shutting oli the ow of air through said cold air passage at predetermined intervals, stopping the circulation of refrigerant to said evaporator plates in the cold vair passage during the period of time that air recirculation is stopped to defrost the refrigeration plates, said shutting off of the air stream and stoppage of the circulation of the refrigerant for defrosting occurring for a short period between short intervals of time and for a longer period between long intervals of time.

8. In the method of refrigeration of ya space which is enclosed except for a vertical side having an access opening of substantial dimension directly communicatingthe interior of the space with the ambient atmosphere, the steps of projecting an inner cold air panel and an outer guard Iair panel in side-by-side, substantially parallel relationship from one edge of the open space to the opposite edge of the open space substantially completely to span the open space with the formed air curtain, separating the cold air panel from the guard air panel at the opposite edge of the open space, recirculating the separated cold air panel through a passage communicating the opposite edge with the one edge ot the open space and recirculating the guard air stream through a separate passage communicating the opposite edge with the one edge across the open space, projecting evaporator plates within each of said passages whereby the recirculating air streams pass in heat exchange relationship with said evaporator plates, circulating a refrigerant through the evaporator plate in the cold air passage to reduce the temperature of the cold air recirculated therethrough, shutting oft' the ilow of air through said cold air passage at predetermined intervals, stopping the circulation of refrigerant to said evaporator plates in the cold air passage during the period of time that air recirculation is stopped to defrost the refrigeration plates, said shutting off of the air stream and stoppage of the circulating of the refrigerant for defrosting occurring for a short period between short intervals of time and for a lonUer period between long intervals of time, and including the introduction of refrigeration plates within the passage through which the guard air stream is recirculated and which includes the step of circulating refrigerant to the refrigeration coils in the guard air passage only for a short period of time in -advance of the shut-0E of vhow of refrigerant to the refrigeration plates in the cold air passage to reduce the temperature of the air making up the guard air stream for reduction of the amount of frost formation on the refrigeration coils in the cold air passage.

`9. The method yas claimed in claim 8 in which the defrost of the refrigeration plates in the guard air stream is achieved by the warmer guard air recirculated through the guard air passage during normal operation before circulation of refrigerant through the refrigeration plates in the guard air passage.

10. The method as claimed in claim 4 including the step of providing an auxiliary supply of refrigerant liquid, said auxiliary supply forming at least a portion of the liquid refrigerant which is converted to hot exhaust vapors for circulation through the refrigerating coils during the defrosting step.

References Cited in the tile of this patent UNITED STATES PATENTS 2,196,291 Clancy Apr. 9, 1940 2,526,379 Maseritz Oct. 17, 1950 3,063,252 Lamb Nov. 13, 1962 3,063,254 Dickson Nov. 13, 1962 

1. IN THE METHOD OF REFRIGERATION OF A SPACE WHICH IS ENCLOSED EXCEPT FOR A SIDE HAVING AN ACCESS OPENING DIRECTLY COMMUNICATING THE INTERIOR OF THE SPACE WITH THE AMBIENT ATMOSPHERE, THE STEPS OF CIRCULATING INNER AND OUTER AIR PANELS IN SIDE-BY-SIDE, SUBSTANTIALLY PARALLEL RELATIONSHIP ACROSS THE OPEN SPACE FROM ONE EDGE OF THE OPEN SPACE TO THE OPPOSITE EDGE SUBSTANTIALLY COMPLETELY TO SPAN THE OPEN SPACE WITH THE FORMED AIR CURTAIN, SEPARATING THE AIR PANELS UPON REACHING THE OPPOSITE EDGE, RECIRCULATING THE SEPARATED AIR PANELS FROM THE OPPOSITE EDGE BACK TO THE ONE EDGE, PASSING THE RECIRCULATING INNER PANEL OF AIR IN HEAT EXCHANGE RELATIONSHIP WITH REFRIGERATION COILS THROUGH WHICH A REFRIGERANT IS CIRCULATED TO REDUCE THE TEMPERATURE OF THE AIR MAKING UP THE INNER PANEL TO A COLD AIR STREAM, PERIODICALLY BETWEEN RELATIVELY SHORT INTERVALS OF TIME STOPPING THE CIRCULATION OF THE AIR PANELS AND FOR A SHORT PERIOD OF TIME WHILE THE CIRCULATION OF THE AIR PANELS IS STOPPED, DEFROSTING THE REFRIGERATION COILS, AND PERIODICALLY BETWEEN RELATIVELY LONG INTERVALS OF TIME STOPPING THE CIRCULATION OF THE AIR PANELS AND FOR A RELATIVELY LONG PERIOD OF TIME DEFROSTING THE REFRIGERATION COILS. 